The present invention relates to a projectile for a centrifugal launching device.
Centrifugal launching devices or launchers have been known since more than a century in different fields; shotblasting machines, sports, toys, armaments.
The present invention only relates to the field of armaments.
In this field high initial speeds (800 m/s and more) are required at present.
In order to obtain such high speeds while keeping the dimensions of the launcher relatively compact, it is necessary to subject the projectile to the centrifugal or radial acceleration and to the Coriolis acceleration which is perpendicular to the first one. So, the resulting speed is composed of a radial speed and a tangential speed, both speeds being perpendicular to each other.
It results therefrom that a gun-vane launcher is preferred, an example of which is described in an other patent application of the Applicant, filed on even date herewith (Ser. No. 521,013 for a "Rotor for Centrifugal Launching Device" filed on Aug. 9, 1983, a continuation of Ser. No. 326,003 filed on Nov. 30, 1981, now abandoned).
A strict exactness of the initial trajectory is of course required; this involves considerable difficulties on the level of the feeding, that has to be rigorous as well, both in place and in time.
For this reason the large majority of proposed solutions these days appeal to spherical projectiles or balls.
Well then, the combination of a rotational speed and a radial speed brings about a so-called Coriolis acceleration.
By way of example, calculations show that for a steel ball of 20 mm across (steel with an average admissible stress of 100 kg/mm.sup.2), launched by a 475 mm gunvane so as to obtain an initial speed of 800 m/s, the Coriolis force attains 4400 kg.
The Herz contact would in these conditions provoque a deformation of the ball in a meridial plane with an area of 44 mm.sup.2.
As this is inadmissible it is clear that the muzzle speed should be limited to far below 500 m/s.
Thus the spherical shape should be rejected for a modern projectile, the more as it is difficult to see how a projectile of this shape could be equipped with an impact rocket explosive charge.
So, the object of the invention is to provide a projectile as resemblant as possible to projectiles of conventional arms, but adapted for being efficiently used in a centrifugal machine equipped with a gun-vane.
This objective is achieved, according to the invention, by a projectile of the ogival head-type, with a body and a tail of decreasing section, characterized in that the body is cylindrical and that the weight of the tail is chosen in such way that the center of gravity of the projectile lays in a plane where the cylindrical body connects to the tail or in the immediate vicinity of this plane, whereas the shape of the said tail is chosen so that no point of the surface of the latter touches the wall of the gun-vane, particularly during the ejection of the projectile.
According to the invention the cylindrical body of the projectile is intended to take up the Coriolis force, which in any point is represented by: EQU F.sub.t =Km.omega..sup.2 rf(.eta.)
wherein:
K is a constant, PA1 m is the mass of the projectile, PA1 .omega. the angular speed of the projectile, PA1 r the radius of the point considered, PA1 f(.eta.) is a function of the coefficient of friction.
For a projectile of 122 g, ejected at 800 m/s by a gun-vane (20 mm calibre) with a length of 475 mm, with an .eta.=0.2, the Coriolis force attains 16427 kg.
So one sees the importance of the cylindrical shape of the body according to the invention.
The double condition of the position of the centre of gravity of the projectile and of the shape of the tail avoids any tilting of the projectile during launching.